This invention relates to hybrid propulsion systems for vehicles, and in particular to a thermal engine in hybrid electrical propulsion systems. In order to improve the range of an efficient electrical propulsion system, the inclusion of virtually pollutionless thermal engines has been proposed. The hybrid propulsion system is a combination between a thermal engine and an associated electric transmission and storage system. The combined system depends on the efficiency, cost effectiveness and complimentary advantages of each technology with avoidance of any technology-specific disadvantages.
The efficiency of thermal engines, in particular internal combustion engines is compromised by the requirement that the engine operate efficiently under vastly different load and demand conditions. However, with the advent of improved electrical storage systems in the form of advanced battery designs and high density capacitors, a power surge can be instantaneously and effectively delivered to a drive motor to respond to changes in power demand and load. With the thermal engine largely insulated from the instantaneous variations in required performance, the design criteria for the thermal engine can be directed at optimizing the efficiency within the narrow performance range required to replenish electrical power reserves.